Butter the bottom of a 9 x 13" baking pan and line with graham crackers.
Mix the milk and pudding for 2 minutes on medium speed, then blend in Cool Whip. Pour 1/2 the mixture over the graham crackers, then place a 2nd layer of graham crackers over the pudding mixture. Pour remaining pudding mixture over graham crackers, then cover with a 3rd layer of graham crackers. Refrigerate for 2 hours.
In a small saucepan, melt the chocolate and add the Karo syrup, vanilla and butter. You can melt the chocolate in the microwave if you don't want to turn your stove on . Mix in powdered sugar and milk, blending until smooth. Spread chocolate mixture over cake and refrigerate at least 6 hours, preferably overnight.
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